This proposal describes a career development plan and research proposal for Dr. Max O'Donnell, a pulmonologist at Albert Einstein College of Medicine. Working with collaborators and mentors at Einstein and in South Africa, Dr. O'Donnell is establishing himself as a translational investigator in drug-resistant tuberculosis (TB) and HIV research. Nowhere has drug-resistant TB generated more alarm than in South Africa, where synergies between endemic TB and HIV have caused 'explosive' increases in TB incidence and case-fatality rates. The most resistant form of TB, extensively drug resistant tuberculosis (XDR-TB), is increasingly prevalent in South Africa. An important obstacle to improving survival for XDR-TB is lack of a rapid, biomarker to serve as a surrogate outcome in clinical trials and guide clinician's by measuring treatment response. Fluoromycobacteriophage (FMP) assays use genetically modified mycobacteria-specific viruses to quantify viable M tuberculosis (Mtb) using a fluorescence reporter system. Utilizing a novel FMP assay with superior test characteristics, Dr. O'Donnell proposes to measure decrease in Mtb in XDR-TB patients' sputum as a biomarker for treatment response (Aim 1). Among XDR-TB patients who fail to respond to treatment Dr. O'Donnell proposes to use the same assay to rapidly diagnose emergent second-line drug resistance (Aim 2). This research component of this proposal is a result of an ongoing funded collaboration between researchers at Albert Einstein College of Medicine with researchers at the KwaZulu-Natal Research Institute for Research in Tuberculosis and HIV/AIDS (K-RITH), and the Centre for AIDS Programme of Research in South Africa (CAPRISA). The training component of this proposal involves developing the applicant as a TB molecular epidemiologist including training in the mentor's laboratory, coursework, seminars, lectures, and specific training in drug-resistant TB microbiology. Unique features include co-mentoring from a renowned TB basic scientist, TB epidemiologist, and translational researcher with additional support from career development committee with extensive TB and career development experience. This is an innovative approach with the potential to make substantial impact in our ability to rationally manage drug-resistant tuberculosis, rapidly evaluate the comparative efficacy of different drug regimens, and rapidly diagnose emergent drug-resistance among TB patients on treatment. This research will form the basis for a prospective study of the application of clinical biomarkers for treatment outcome in drug-resistant tuberculosis that will be proposed in an R01 grant application before the end of the K award.